A plurality of processes including machining, airtightness detection, spraying and the like are needed from a wheel blank to an available finished product. In the machining process, the wheel blank is usually machined in three steps. The existing first-step fixture, second-step fixture and three-step fixture are not the same in structure, but they have a common feature that the fixtures may only be applied to wheels of a fixed size compatible with their sizes. If wheels of another size are to be machined, a few groups of positioning and clamping mechanisms need to be replaced, which increases the production assistance time of the workshop, reduces the production efficiency and increases the labor intensity of workers. In addition, the existing first-step fixture and second-step fixture adopt too heavy balance blocks for balancing the centrifugal force of fixture rotating bodies. If the rotating speed of a machine tool spindle is to be improved to increase the production efficiency, upper structure of the fixture will bear a large centrifugal force, which is even beyond safe use condition of the fixture.